/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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/*
 *
 *
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 *
 *
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent;

import java.util.Collection;
import java.util.Set;
import java.util.AbstractSet;
import java.util.Iterator;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Predicate;
import java.util.function.Consumer;

/**
 * A {@link java.util.Set} that uses an internal {@link CopyOnWriteArrayList}
 * for all of its operations.  Thus, it shares the same basic properties:
 * <ul>
 * <li>It is best suited for applications in which set sizes generally
 * stay small, read-only operations
 * vastly outnumber mutative operations, and you need
 * to prevent interference among threads during traversal.
 * <li>It is thread-safe.
 * <li>Mutative operations ({@code add}, {@code set}, {@code remove}, etc.)
 * are expensive since they usually entail copying the entire underlying
 * array.
 * <li>Iterators do not support the mutative {@code remove} operation.
 * <li>Traversal via iterators is fast and cannot encounter
 * interference from other threads. Iterators rely on
 * unchanging snapshots of the array at the time the iterators were
 * constructed.
 * </ul>
 *
 * <p><b>Sample Usage.</b> The following code sketch uses a
 * copy-on-write set to maintain a set of Handler objects that
 * perform some action upon state updates.
 *
 * <pre> {@code
 * class Handler { void handle(); ... }
 *
 * class X {
 *   private final CopyOnWriteArraySet<Handler> handlers
 *     = new CopyOnWriteArraySet<Handler>();
 *   public void addHandler(Handler h) { handlers.add(h); }
 *
 *   private long internalState;
 *   private synchronized void changeState() { internalState = ...; }
 *
 *   public void update() {
 *     changeState();
 *     for (Handler handler : handlers)
 *       handler.handle();
 *   }
 * }}</pre>
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @param <E> the type of elements held in this collection
 * @author Doug Lea
 * @see CopyOnWriteArrayList
 * @since 1.5
 */
public class CopyOnWriteArraySet<E> extends AbstractSet<E>
    implements java.io.Serializable {

  private static final long serialVersionUID = 5457747651344034263L;

  private final CopyOnWriteArrayList<E> al;

  /**
   * Creates an empty set.
   */
  public CopyOnWriteArraySet() {
    al = new CopyOnWriteArrayList<E>();
  }

  /**
   * Creates a set containing all of the elements of the specified
   * collection.
   *
   * @param c the collection of elements to initially contain
   * @throws NullPointerException if the specified collection is null
   */
  public CopyOnWriteArraySet(Collection<? extends E> c) {
    if (c.getClass() == CopyOnWriteArraySet.class) {
      @SuppressWarnings("unchecked") CopyOnWriteArraySet<E> cc =
          (CopyOnWriteArraySet<E>) c;
      al = new CopyOnWriteArrayList<E>(cc.al);
    } else {
      al = new CopyOnWriteArrayList<E>();
      al.addAllAbsent(c);
    }
  }

  /**
   * Returns the number of elements in this set.
   *
   * @return the number of elements in this set
   */
  public int size() {
    return al.size();
  }

  /**
   * Returns {@code true} if this set contains no elements.
   *
   * @return {@code true} if this set contains no elements
   */
  public boolean isEmpty() {
    return al.isEmpty();
  }

  /**
   * Returns {@code true} if this set contains the specified element.
   * More formally, returns {@code true} if and only if this set
   * contains an element {@code e} such that
   * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
   *
   * @param o element whose presence in this set is to be tested
   * @return {@code true} if this set contains the specified element
   */
  public boolean contains(Object o) {
    return al.contains(o);
  }

  /**
   * Returns an array containing all of the elements in this set.
   * If this set makes any guarantees as to what order its elements
   * are returned by its iterator, this method must return the
   * elements in the same order.
   *
   * <p>The returned array will be "safe" in that no references to it
   * are maintained by this set.  (In other words, this method must
   * allocate a new array even if this set is backed by an array).
   * The caller is thus free to modify the returned array.
   *
   * <p>This method acts as bridge between array-based and collection-based
   * APIs.
   *
   * @return an array containing all the elements in this set
   */
  public Object[] toArray() {
    return al.toArray();
  }

  /**
   * Returns an array containing all of the elements in this set; the
   * runtime type of the returned array is that of the specified array.
   * If the set fits in the specified array, it is returned therein.
   * Otherwise, a new array is allocated with the runtime type of the
   * specified array and the size of this set.
   *
   * <p>If this set fits in the specified array with room to spare
   * (i.e., the array has more elements than this set), the element in
   * the array immediately following the end of the set is set to
   * {@code null}.  (This is useful in determining the length of this
   * set <i>only</i> if the caller knows that this set does not contain
   * any null elements.)
   *
   * <p>If this set makes any guarantees as to what order its elements
   * are returned by its iterator, this method must return the elements
   * in the same order.
   *
   * <p>Like the {@link #toArray()} method, this method acts as bridge between
   * array-based and collection-based APIs.  Further, this method allows
   * precise control over the runtime type of the output array, and may,
   * under certain circumstances, be used to save allocation costs.
   *
   * <p>Suppose {@code x} is a set known to contain only strings.
   * The following code can be used to dump the set into a newly allocated
   * array of {@code String}:
   *
   * <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
   *
   * Note that {@code toArray(new Object[0])} is identical in function to
   * {@code toArray()}.
   *
   * @param a the array into which the elements of this set are to be stored, if it is big enough;
   * otherwise, a new array of the same runtime type is allocated for this purpose.
   * @return an array containing all the elements in this set
   * @throws ArrayStoreException if the runtime type of the specified array is not a supertype of
   * the runtime type of every element in this set
   * @throws NullPointerException if the specified array is null
   */
  public <T> T[] toArray(T[] a) {
    return al.toArray(a);
  }

  /**
   * Removes all of the elements from this set.
   * The set will be empty after this call returns.
   */
  public void clear() {
    al.clear();
  }

  /**
   * Removes the specified element from this set if it is present.
   * More formally, removes an element {@code e} such that
   * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>,
   * if this set contains such an element.  Returns {@code true} if
   * this set contained the element (or equivalently, if this set
   * changed as a result of the call).  (This set will not contain the
   * element once the call returns.)
   *
   * @param o object to be removed from this set, if present
   * @return {@code true} if this set contained the specified element
   */
  public boolean remove(Object o) {
    return al.remove(o);
  }

  /**
   * Adds the specified element to this set if it is not already present.
   * More formally, adds the specified element {@code e} to this set if
   * the set contains no element {@code e2} such that
   * <tt>(e==null&nbsp;?&nbsp;e2==null&nbsp;:&nbsp;e.equals(e2))</tt>.
   * If this set already contains the element, the call leaves the set
   * unchanged and returns {@code false}.
   *
   * @param e element to be added to this set
   * @return {@code true} if this set did not already contain the specified element
   */
  public boolean add(E e) {
    return al.addIfAbsent(e);
  }

  /**
   * Returns {@code true} if this set contains all of the elements of the
   * specified collection.  If the specified collection is also a set, this
   * method returns {@code true} if it is a <i>subset</i> of this set.
   *
   * @param c collection to be checked for containment in this set
   * @return {@code true} if this set contains all of the elements of the specified collection
   * @throws NullPointerException if the specified collection is null
   * @see #contains(Object)
   */
  public boolean containsAll(Collection<?> c) {
    return al.containsAll(c);
  }

  /**
   * Adds all of the elements in the specified collection to this set if
   * they're not already present.  If the specified collection is also a
   * set, the {@code addAll} operation effectively modifies this set so
   * that its value is the <i>union</i> of the two sets.  The behavior of
   * this operation is undefined if the specified collection is modified
   * while the operation is in progress.
   *
   * @param c collection containing elements to be added to this set
   * @return {@code true} if this set changed as a result of the call
   * @throws NullPointerException if the specified collection is null
   * @see #add(Object)
   */
  public boolean addAll(Collection<? extends E> c) {
    return al.addAllAbsent(c) > 0;
  }

  /**
   * Removes from this set all of its elements that are contained in the
   * specified collection.  If the specified collection is also a set,
   * this operation effectively modifies this set so that its value is the
   * <i>asymmetric set difference</i> of the two sets.
   *
   * @param c collection containing elements to be removed from this set
   * @return {@code true} if this set changed as a result of the call
   * @throws ClassCastException if the class of an element of this set is incompatible with the
   * specified collection (optional)
   * @throws NullPointerException if this set contains a null element and the specified collection
   * does not permit null elements (optional), or if the specified collection is null
   * @see #remove(Object)
   */
  public boolean removeAll(Collection<?> c) {
    return al.removeAll(c);
  }

  /**
   * Retains only the elements in this set that are contained in the
   * specified collection.  In other words, removes from this set all of
   * its elements that are not contained in the specified collection.  If
   * the specified collection is also a set, this operation effectively
   * modifies this set so that its value is the <i>intersection</i> of the
   * two sets.
   *
   * @param c collection containing elements to be retained in this set
   * @return {@code true} if this set changed as a result of the call
   * @throws ClassCastException if the class of an element of this set is incompatible with the
   * specified collection (optional)
   * @throws NullPointerException if this set contains a null element and the specified collection
   * does not permit null elements (optional), or if the specified collection is null
   * @see #remove(Object)
   */
  public boolean retainAll(Collection<?> c) {
    return al.retainAll(c);
  }

  /**
   * Returns an iterator over the elements contained in this set
   * in the order in which these elements were added.
   *
   * <p>The returned iterator provides a snapshot of the state of the set
   * when the iterator was constructed. No synchronization is needed while
   * traversing the iterator. The iterator does <em>NOT</em> support the
   * {@code remove} method.
   *
   * @return an iterator over the elements in this set
   */
  public Iterator<E> iterator() {
    return al.iterator();
  }

  /**
   * Compares the specified object with this set for equality.
   * Returns {@code true} if the specified object is the same object
   * as this object, or if it is also a {@link Set} and the elements
   * returned by an {@linkplain Set#iterator() iterator} over the
   * specified set are the same as the elements returned by an
   * iterator over this set.  More formally, the two iterators are
   * considered to return the same elements if they return the same
   * number of elements and for every element {@code e1} returned by
   * the iterator over the specified set, there is an element
   * {@code e2} returned by the iterator over this set such that
   * {@code (e1==null ? e2==null : e1.equals(e2))}.
   *
   * @param o object to be compared for equality with this set
   * @return {@code true} if the specified object is equal to this set
   */
  public boolean equals(Object o) {
    if (o == this) {
      return true;
    }
    if (!(o instanceof Set)) {
      return false;
    }
    Set<?> set = (Set<?>) (o);
    Iterator<?> it = set.iterator();

    // Uses O(n^2) algorithm that is only appropriate
    // for small sets, which CopyOnWriteArraySets should be.

    //  Use a single snapshot of underlying array
    Object[] elements = al.getArray();
    int len = elements.length;
    // Mark matched elements to avoid re-checking
    boolean[] matched = new boolean[len];
    int k = 0;
    outer:
    while (it.hasNext()) {
      if (++k > len) {
        return false;
      }
      Object x = it.next();
      for (int i = 0; i < len; ++i) {
        if (!matched[i] && eq(x, elements[i])) {
          matched[i] = true;
          continue outer;
        }
      }
      return false;
    }
    return k == len;
  }

  public boolean removeIf(Predicate<? super E> filter) {
    return al.removeIf(filter);
  }

  public void forEach(Consumer<? super E> action) {
    al.forEach(action);
  }

  /**
   * Returns a {@link Spliterator} over the elements in this set in the order
   * in which these elements were added.
   *
   * <p>The {@code Spliterator} reports {@link Spliterator#IMMUTABLE},
   * {@link Spliterator#DISTINCT}, {@link Spliterator#SIZED}, and
   * {@link Spliterator#SUBSIZED}.
   *
   * <p>The spliterator provides a snapshot of the state of the set
   * when the spliterator was constructed. No synchronization is needed while
   * operating on the spliterator.
   *
   * @return a {@code Spliterator} over the elements in this set
   * @since 1.8
   */
  public Spliterator<E> spliterator() {
    return Spliterators.spliterator
        (al.getArray(), Spliterator.IMMUTABLE | Spliterator.DISTINCT);
  }

  /**
   * Tests for equality, coping with nulls.
   */
  private static boolean eq(Object o1, Object o2) {
    return (o1 == null) ? o2 == null : o1.equals(o2);
  }
}
